Argentine scientists agree that there are signs of recovery of the ozone layer that protects life on earth by filtering out the sun’s harmful ultraviolet radiation, but they are cautious about saying that the problem is on its way to a solution.
“This year was benign, but the problem has not been solved. The ozone hole could expand to a record size in 2013,” Gerardo Carbajal, head of the Department of Atmospheric Monitoring and Geophysics (VAyGEO), said.
According to Carbajal, whose department is part of the National Meteorological Service, “this year the ozone hole was one of the smallest ever and it closed up earlier than expected, but we’ll have to wait and see before we can speak of a trend.”
Similarly, Susana Díaz, an engineer with the Southern Centre for Scientific Research (CADIC), said that “in recent years we have observed a slight decrease of the ozone deficit within the so-called ‘hole’.”
Díaz is a member of the state National Scientific and Technical Research Council (CONICET) and heads the CADIC Ozone and Ultraviolet Radiation Laboratory in Ushuaia, the capital of the province of Tierra del Fuego, the most southerly in the country.
Measurements are made there of the ultraviolet rays that filter down over the city, to record the impact of the radiation during the season of ozone hole expansion in the stratosphere, which occurs from September to mid-November.
Ozone is a gas in the stratosphere, between 15 and 35 kilometres above the earth’s surface, which protects the biosphere by absorbing UV rays that are harmful to human health and plant and animal life.
Exposure to high levels of UV radiation can cause a higher incidence of skin cancer and eye problems in the population of affected areas, like southern Argentina and Chile.
“This year the ozone hole season was much shorter than in earlier years, and lasted only two days above Ushuaia. In other seasons it has lasted for 10 days, and it has been felt further north, in Patagonia,” said Guillermo Deferrari, a biologist at CADIC.
The size of the ozone hole varies. Some years it has covered an area of 30 million square kilometres, but in the last few weeks it has extended over 22 million square kilometres – still an area larger than all of South America.
According to the scientific consensus, the thinning of the ozone layer over Antarctica was mainly due to the use of chlorofluorocarbons (CFCs), chemical substances used in the manufacturing of aerosols and refrigerants.
When this evidence was confirmed in the 1970s, countries signed the Vienna Convention for the Protection of the Ozone Layer, and in 1987 they approved the Montreal Protocol. These treaties were ratified by the largest number ever of United Nations members and set a timetable for phasing out and eliminating CFCs.
Twenty-five years after the Montreal Protocol was approved, industry has substituted CFCs by hydrofluorocarbons (HFCs) which, while they do not harm the ozone layer, are greenhouse gases and contribute to global warming.
Meanwhile, there are other substances that destroy ozone and have not been replaced, such as methyl bromide, a pesticide, which in the Protocol is only scheduled for complete elimination in 2015.
Deferrari, who operates equipment at CADIC for measuring UV radiation over Ushuaia, said that “the levels are stable now, with no observed increase in the destruction of the ozone layer.”
He agreed with colleagues that this improvement cannot be said to be a trend, and that the ozone hole could grow again next year, because it depends on meteorological conditions in Antarctica as well. He said, however, that there are clear “signs of recovery”.
The observations confirm the findings of the latest report on the issue by the United Nations Environment Programme (UNEP) and World Meteorological Organisation (WMO), published in 2010.
The study, Scientific Assessment of Ozone Depletion 2010, concluded that CFC elimination was having an effect and the ozone hole was not growing – a sign of recovery.
However, Deferrari pointed out that “we have not yet returned to the radiation levels we had in 1980,” since the chemicals that destroy ozone take 10 years to reach the stratosphere, and then the ozone layer takes time to recover.
Complete recovery of stratospheric ozone over Antarctica will take another 40 to 60 years, different studies say. But the fact that this year’s hole is smaller is good news.
A version of this article was first publish by Inter Press Service news agency (IPS).